1. Field of the Invention
The present invention relates to a lens barrel having a shake-correcting function, and an optical device having the same.
2. Description of the Related Art
In order to prevent image blur due to hand shake or the like caused when a camera is held in the hand, various devices have been proposed which perform hand shake correction by detecting information about the shaking of the camera by shake-detecting means and optically or electronically cancelling the hand shake according to the result of the detection. For example, Japanese Patent Application No. 10-109499 and U.S. Pat. No. 6,112,028 corresponding thereto disclose a zoom lens having a so-called shift-type shake-correction means which corrects hand shake by moving one of a plurality of lens units in a plane perpendicular to the optical axis.
In this disclosure, three pins are press-fitted in a barrel for holding a shift lens unit so as to be arranged in the radial direction, and are fitted in three slots formed in a fixed member in the circumferential direction with a certain clearance therebetween, thereby regulating the shift lens unit in a plane perpendicular to the optical axis. Furthermore, a guide section is urged in one direction by a magnetic attracting force acting between a magnet and a ferromagnetic material so as to be prevented from rattling in the optical axis direction. This makes it possible to enhance optical performance and to reduce operating noise resulting from rattling during driving.
Japanese Patent Laid-Open No. 6-289465 and U.S. Pat. No. 5,602,675 corresponding thereto disclose a shake-correcting device in which loads in the optical axis direction and two shift direction are reduced by appropriately designing the shape and layout of extension parts of a flexible printed circuit board for connecting a fixed section and a shifting section, thereby preventing the driving of the shifting section from being adversely affected by the loads.
Japanese Patent Laid-Open No. 10-319465 and U.S. Pat. No. 6,064,827 corresponding thereto disclose a lens shifting device, in which, in order to prevent rattling of a guide section in the optical axis direction and to reduce driving resistance with a simple structure, at least three balls are clamped by springs between a fixed member and a movable member, and the movable member is guided by rolling balls and is prevented by the springs from rotating about the optical axis.
Recent optical devices having a lens barrel have been required to become more compact and to have less protuberances in order to improve portability and ease of mounting. With this, of course, there has been a demand for reducing the size of the lens barrel. If the lens barrel is further reduced in size, however, the space for accommodating a flexible printed circuit board for connecting a fixed section and a movable section is substantially limited, and rigidity of the flexible printed circuit board is increased. As a result, as taught in Japanese Patent Laid-Open No. 6-289465, it is difficult to reduce the force produced in the flexible printed circuit board in the optical axis direction to such a level that the force is not significant by only changing the shape and layout of the extension parts.
Accordingly, there has been a proposal to urge the movable section in the optical axis direction by an appropriate force produced by a magnet or the like, as disclosed in Japanese Patent Application No. 10-109499. However, depending on variations in urging force in the optical axis direction produced in the flexible printed circuit board, the movable section is more strongly pressed against the guide section and friction is significantly increased, or conversely, urging by the magnet or the like is cancelled. This adversely affects the driving of the movable section.
On the other hand, because of advances in semiconductor micromachining technologies, it has been possible to produce CCDs with a smaller pixel pitch which convert an image of a subject formed in the focal plane by an image-capturing optical system into electrical signals. This has led to two trends: further size reduction of the optical system by arranging the same number of pixels as previously in a smaller area, and higher resolution of the optical system achieved by arranging more pixels in the same area and in a larger area. In the former, since the amount of shift of a shift lens unit for correcting hand shake is substantially proportional to the image-capturing area, more precise motion is needed, and the space for accommodating the flexible printed circuit board is reduced. In the latter case, since the resolution is lowered unless a smaller shake can be corrected, it is necessary to reduce frictional force produced in a guide section for the movable section and to thereby achieve more precise motion. In both cases, the required accuracy of tilting of the shift lens unit is increased.
Japanese Patent Laid-Open No. 10-319465 discloses a structure in which at least three balls are clamped between the fixed member and the movable member by the tensile force of the springs, and the movable member is guided by rolling the balls in order to prevent the guide section from rattling in the optical axis direction and to thereby reduce friction. Since the balls are held by a holding member so as not to be displaced from the fixed member, the movable member is guided by rolling the balls. Sliding frictional force is generated between the balls and the fixed member and the holding member due to the rolling of the balls in the holding member, and therefore, the balls are clamped by the smallest possible urging force of the springs which prevents rattling of the balls. For this reason, the movable member is lifted by a slight acceleration in the optical axis direction in which an inertial force greater than the urging force acts on the movable member. Consequently, optical performance is degraded due to tilting of the lens unit, and noise, such as sound generated by the abutting movement of the balls, is produced. For example, when a movable member of 4 g is urged by a force of 4 gf, it is lifted only by an acceleration of 1 G or more.
Since the movable member is prevented from rotating about the optical axis only by the tensile force of the springs, the rotation cannot be prevented completely, but is only restrained. In the above proposal, since the output value from a position detecting means is changed due to the rotation about the optical axis, the movable member may be rotated about the optical axis depending on the positional relationship between the position where the driving means generates force and the center of gravity of the movable member and on the connecting position and shape of the flexible printed circuit board. This makes it impossible to precisely move the shift lens to the correct position for shake correction.
Accordingly, an object of the present invention is to provide a lens barrel in which load is applied to a movable member during driving only by a force produced by rolling friction of balls, which is considerably smaller than the sliding frictional force, until the balls each contact a limiting end of a limited range, in which a lens unit for shake correction can be precisely driven even when force for urging the movable member in the optical direction is increased, and in which the urging force can be increased to such a degree that the influence of variations in force in the optical axis direction generated in a flexible printed circuit board for connecting the movable member and a fixed member is negligible, thereby preventing rattling more reliably.
Another object of the present invention is to provide an optical device in which a relative movement between a movable member and a fixed member is supportingly guided only by rolling of balls in actual use, frictional force is minimized during shake correction, and superior shake-correction performance can be obtained.
A further object of the present invention is to provide a lens barrel in which load is applied to a holding member during driving only by a force produced by rolling friction of balls, which is considerably smaller than the sliding frictional force, until the balls each contact a limiting end of a limited range, in which a lens unit for shake correction can be precisely driven even when force for urging the holding member in the optical direction is increased, and in which the urging force can be increased to such a degree that the influence of variations in force in the optical axis direction generated in a flexible printed circuit board for connecting the holding member and a support base is negligible, thereby preventing rattling more reliably.
In order to achieve the above objects, according to an aspect of the present invention, there is provided a lens barrel having an optical axis and including: a lens movable in a direction orthogonal to the optical axis to correct image shake; a movable member that holds the lens; a fixed member that regulates movement of the movable member in a direction of the optical axis; at least three balls placed between the movable member and the fixed member, the balls being held in respective holding portions formed in the movable member or the fixed member so as to roll and to allow a relative movement between the movable member and the fixed member; an urging member that urges the movable member toward the fixed member; driving means for generating force for moving the movable member in two directions orthogonal to the optical axis; and position detecting means for detecting a position of the movable member in the two directions orthogonal to the optical axis.